South Dakota state law: vehicle noise and muffler requirements

SDCL 32-15-6 (Mufflers required) is the controlling statewide vehicle-noise statute: it requires every motor vehicle operated on a highway to be equipped with a muffler in good working order and in constant operation, and prohibits muffler cutouts, bypasses, or similar devices. The statute does not specify a dBA threshold and does not distinguish between motorcycles, cars, and trucks. Enforcement is by South Dakota Highway Patrol and local police as a Class 2 misdemeanor traffic offense. SDCL Title 32 Chapter 15 covers the statewide motor-vehicle equipment standards (lights, brakes, horns, mufflers). Compression-brake (engine-brake / Jake-brake) restrictions, motorcycle decibel caps, and modified-exhaust enforcement at the local level are authorized under SDCL 9-29-1 (cities) and SDCL Chapter 11-2 (counties on county roads). Typical municipal vehicle-noise caps (set under local police power): 80 dBA at 50 ft for passenger cars and 96 dBA at 50 ft for motorcycles. The Sturgis Motorcycle Rally and broader SD motorcycle-tourism economy create a recognized political baseline against aggressive municipal motorcycle-exhaust enforcement during August.

SDCL 32-15-6 violation: Class 2 misdemeanor traffic offense - up to 30 days in jail and up to a $500 fine. South Dakota Highway Patrol may issue an equipment-violation citation requiring repair and reinspection. Municipal vehicle-noise / engine-brake violations: typically civil fines of $50 to $250 per occurrence under local ordinance.